Cocaine abuse and dependence have disastrous medical and social consequences which have made the development of an effective treatment a high priority (Pan, Y., Gao, D., Yang, W., Cho, H., Yahg, G., Tai, H., Zhan, C., “Computational redesign of human butyrylcholinesterase for anticocaine medication,” PNAS, 102(46):16656-61, 2005). However, as stated by Brimijoin et al.: “there is no reliable means to treat cocaine overdose or reduce the likelihood of relapse in users who have achieved abstinence. Human plasma butyrylcholinesterase (BChE) contributes to normal cocaine metabolism and has been considered for use in treating cocaine toxicity” (Brimijoin, S., Gao, Y., Anker, J., Gliddon, L., LaFleur, D., Shah, R., Zhao, Q., Singh, M., Carroll, M., “A Cocaine Hydrolase Engineered from Human Butyrylcholinesterase Selectively Blocks Cocaine Toxicity and Reinstatement of Drug Seeking in Rats,” Neuropsychopharmacology, 33:2715-25, 2008).
Wild-type BChE, while important for cocaine metabolism in the body, has low catalytic efficiency with cocaine. The low cocaine hydrolase activity of wild-type BChE would require the use of prohibitively large quantities of purified enzyme for treatment of cocaine abuse or overdose. Mutagenesis performed on human BChE with the goal of enhancing the cocaine hydrolase activity resulted in the development of the double mutant A328W/Y332A (residues 356 and 360 relative to full length BChE) that has a kcat that is 40-fold higher than wild-type BChE, with only a slightly increased KM (Sun H., Shen M., Pang Y., Lockridge O., Brimijoin S., “Cocaine Metabolism Accelerated by a Re-Engineered Human Butyrylcholinesterase” Journal of Pharmacology and Experimental Therapeutics, 302(2):710-716, 2002).
Further experimentation utilizing molecular dynamics to simulate the transition state for the first chemical reaction step of BChE catalyzed hydrolysis of cocaine resulted in the BChE mutant A227S/S315G/A356W/Y360G that has a catalytic efficiency which is 500-fold greater than wild-type BChE and is greater than other previously designed BChE mutants (Pan, Y., Gao, D., Yang, W., Cho, H., Yang, G., Tai, H., Zhan, C., “Computational redesign of human butyrylcholinesterase for anticocaine medication,” PNAS, 102(46):16656-61, 2005).
To obtain a form of the A227S/S315G/A356W/Y360G BChE mutant that may be suitable for therapeutic use, the BChE mutant designed by Pan et al. was fused at its C terminus to human serum albumin (HSA) because it has been observed that similar fusions exhibit favorable pharmacokinetic properties with high stability and extended plasma half lives. It was observed that the BChE-albumin fusion comprising the above mutations retains high catalytic efficiency with cocaine and exhibits a plasma half-life of 8 hours after i.v. injection to rats. (Brimijoin S., Cao, Y., Anker J., Gliddon L., LaFleur D., Shah R., Zhao, Q., “A Cocaine Hydrolase Engineered from Human Butyrylcholinesterase Selectively Blocks Cocaine Toxicity and Reinstatement of Drug Seeking in Rats” Neuropsychopharmacology, 33:2715-25, 2008).
To date, there has been no effective method for treating cocaine abuse or overdose in primates developed that utilizes a BChE-albumin fusion comprising the mutations A227S, S315G, A356W, and Y360G.